In reception chains, Low Noise Amplifiers, subsequently called LNAs, pose energy consumption problems. Their significant consumption is mainly related to linearity requirements. One reason for the need for linearity resides in the necessity to limit the saturation as well as the harmonics and the modulation products related to these saturations and non-linearities.
The harmonics are the frequency multiples of the strong signals at n times the initial frequency. In the wideband case these parasitic signals are contained in the useful bandwidth and are troublesome in respect of the processing of the reception output signal. The other known problems are the intermodulation products which are generated in case of non-linearity. They occur in the presence of two weakly frequency-spaced signals. The measurement of these products is characterized by a polynomial expansion based on Taylor series, the third order corresponding to the third product of the Taylor series. The measurement is characterized by this third order and is known by the name IP3 or TOI (Third Order Intercept).
In the case of a wideband amplifier, for example with a ratio of 4, the reception of a strong signal F0 and of a weak signal at another frequency generates harmonics related to distortion, which distortion is caused by the non-linearity of the amplifier. The non-linearity can then be likened to a mixer and may give products of mixing between the frequency of the strong signal and the harmonics: F0+f1, F0+2f1, . . . F0+nf1, . . . . The more significant the bandwidth, the more significant the effect will be.
An operational necessity of LNAs is their robustness in the face of external assaults. The effects of these assaults are often limited by the technology used and the value of the supply voltage. The more significant the supply voltage, the more resistant is the component but the more energy it consumes. This consumption is related to the class of the amplification and to the currents and voltages employed to avoid saturations in the presence of high currents.
The technologies which allow wideband reception and a significant dynamic range are recent, a significant dynamic range corresponding to a wide span of operating values at the input of the LNA. However, these technologies consume a great deal of current if linearity is desired over the whole of the frequency band.
The use of logarithmic amplifiers in radar detectors makes it possible to obtain significant dynamic ranges to the detriment of linearity.
The use of narrowband amplifiers makes it possible to obtain linearities over significant operating spans without being disturbed by the echoes of the harmonics of order 2 and higher, or out-of-useful-band signals.
The need to have multifunction systems, especially so as to minimize antennal apertures, is now a necessity so as to compact the probes. Advances in technology are making it possible to amplify signals occupying a wide frequency band and of large dynamic range.
However, a price to be paid for marrying these two advantages is the consumption of the LNAs which tends to become very considerable when in the presence of an array antenna and when there are as many LNAs as active modules. It is even possible to reach a paradox in the fact that the reception part consumes more than the emission part.